REPORT OF THE DIRECTOR I9IO 



245 



of his p. c h a p m a n i (see upper left-hand region of text figure 

 20) consists of a long, high, large, central, covered epithecal canal 

 with the younger, shorter and smaller canals grouped on either side 

 of it. These all crossed the suture and so form a ridge '' broad at 

 the base, or roof-shaped." The canals themselves Billings calls 

 " deep fissurelike striae " and, as shown by our figure, a " radiating 

 ridge " may consist of a group of seven or eight of these fissurelike 

 striae. His whole description, given in the footnote, tells us only, 

 so far as concerns the descrip- 

 tion of the species, that it ex- 

 hibits " six roof-shaped ridges 

 radiating from the center . . . 

 and increasing in height and 

 width ... as they approach 

 the sides. \\'hen . . . the 

 external surface is worn away, 

 the plates . . . become cov- 

 ered with deep fissurelike striae, 

 like those of P. t e n u i r a d i a - 

 tus." We may express the 

 essence of the description as fol- 

 lows : the plates of P. c h a p - 

 m a n i show^ as many radiating 

 groups of covered canals as 

 there are angles to a plate. The 

 older, central canals are higher fig. 20 From a photomicrograph (xio) of the 



, , , ^ - holotvpe of Palaeocystites chapman i 



and longer and irom these we BUI., now in the Museum of the Geological Sur- 



, 1 . ve}^ of Canada at Ottawa 



may pass down a regular slope 



to the smallest and shortest canal which is always situated next to 

 the angle of a plate. His means of distinguishing between his P. 

 chapman i and P. t e n u i r a d i a t u s Hall is but a means of 

 distinguishing between his P a 1 a e o c r i n u s s t r i a t u s and 

 Hall's Palaeocystites t e n u i r a d i a t u s . 



The holotype consists of a single plate so badly weathered as to 

 lose some portion of the entire surface and very much of that sur- 

 face as the plate margins are approached. A small portion of the 

 sutural faces is also lost. H we examine in detail the figure of the 

 type, here given, we may note the following resemblances to the 

 r.ant.P. of P a 1 a e o c r i n u s s t r i a t u s . 



